There is known a volume pump that transfers a transfer fluid by changing a volume of an inside of a pump chamber by a deformable member such as a bellows or a diaphragm. In this kind of volume pump, a suction valve is provided between a suction port and the pump chamber of the pump, and a discharge valve is provided between a discharge port and the pump chamber of the pump. Now, for example, Patent Document 1 listed below discloses a volume pump having a suction valve and a discharge valve that include: a cylindrical valve seat; and a valve body that slides along an inner wall of this cylindrical valve seat. Moreover, Patent Document 2 listed below discloses a volume pump having a suction valve and a discharge valve that include: a cylindrical valve seat; and a spherical valve body that slides along an inner wall of this valve seat.